The chassis of a railway locomotive includes a pair of longitudinal sills, which disposed along opposite sides of the locomotive. Referring to FIGS. 1A-C, a sill is typically formed by welding a web member W to a flange member F to form an approximately T-shaped cross section. Intentionally, the completed sill is not straight. Typically, it is desired that the sill have predetermined amounts of camber, sweep, and tilt.
Camber refers to the curvature of the sill in a plane corresponding to the web, which is often measured as a linear deviation of the sill from an imaginary straight line extending between the ends of the sill, as may be seen in FIG. 1B. Typical locomotive specifications require a camber of up to about 5 inches, measured at the midpoint of the sill, which may be 40 feet long.
Sweep refers to the curvature of the sill in a plane corresponding to the flange, which is often measured as a linear deviation of the sill from an imaginary straight line extending between the ends of the sill, as may be seen in FIG. 1C. Typical locomotive specifications require a sweep of up to about ⅝ inch, measured at the midpoint of the sill.
Tilt refers to the difference between 90 degrees and the actual angle between the web and the flange. As may be seen in FIG. 1A, the tilt is often expressed as a linear deviation of the sill from an imaginary straight line extending 90 degrees to the plane of the flange. Typical locomotive specifications permit a tilt tolerance of about ¼ inch, which is typically measured using a calibrated square at the base of the sill.
Typically, a locomotive sill is assembled using the following process. Firstly, the web and flange are mounted on a support beam, in the desired orientation relative to each other and tacked together by short welds. The two pieces are then welded together, for example using at a pull through double head sub arc welding machine. Due to the thermal stresses of the welding process, the welded sill is typically warped in all three planes, so that the tilt, sweep and camber all lie outside of allowable tolerances for the finished sill. In this case, the welded sill is heat treated by experienced repairmen to further warp the sill until the tilt, sweep and camber all lie within the allowable tolerances. Finally, the treated sill is sent to a detailing area where drills and torches are used by experienced tradesmen to manually cut the holes and end contours required by the design specifications of the sill.
This process is both labour intensive and does not yield easily reproducible results, in that, while each completed sill lies within acceptable tolerances, it is very difficult to produce two identical sills. Similar considerations apply in welding other large structural elements where the relative disposition of a pair of plates must meet specified tolerances after the welding process.
A process for manufacturing such structures that overcomes deficiencies in the prior art, would be highly desirable.